This invention relates to an improved process for the manufacture of hydrocarbon conversion catalysts comprising halided aluminas. More particularly this invention relates to a novel high-activity chlorided alumina catalyst for use in the polymerization of mixed butene streams, containing substantial proportions of isobutene, to yield high-viscosity polybutenes.
Halided alumina catalysts have been used in a variety of hydrocarbon conversion processes, as diverse as isomerization, reforming and hydrofining, optionally combined with other catalytic agents. Such catalysts, for use in olefin polymerization, are extensively described in U.S. Pat. No. 4,288,649, which is expressly incorporated herein by reference.
A major problem in the polymerization of olefins, to provide components for lubricant and other petrochemical compositions, has been the effective and economic removal of heat of reaction. Expensive refrigeration systems are required to permit polymerization to proceed at preferred temperatures ranging from about 30.degree. to about 100.degree. F. At the higher temperatures, product viscosity decreases markedly. At the desired lower temperatures, the polymerization reaction is more selective for the isobutene in the mixed butene feed.
Existing technology employing aluminum chloride catalyst in a stirred tank requires extensive cooling and also characteristically forms a "red oil" phase which consumes a significant quantity of olefin. The newer technology employing halided alumina, particularly chlorided alumina, in a fixed bed permits operation at temperatures of about 100.degree. F. Refrigeration requirements are less but the yield of desirable polymer tends to be low.
Even though improved polymerization results can be obtained at lower cost employing the halided alumina catalysts, there remains a need for an economically attractive polymerization process for affording high yields of suitable viscous polymer. Particularly attractive would be process conditions requiring no refrigeration, whereby effective cooling could be achieved by the sole use of ambient temperature cooling water.
The known halided alumina catalysts are prepared by heating a gamma-alumina base in the presence of a haliding agent at a temperature within the range from 200.degree. to about 1100.degree. F. One suitable haliding agent comprises about 4 vol. % carbon tetrachloride in a stream of air or argon. By this technique a chloride content of about 6 to 9 wt. % is generated on the catalyst. This technique apparently does not generate aluminum chloride but rather operates to replace oxygen atoms and hydroxyl groups on the alumina surface with halide atoms in a random manner.